The potential environmental impact of the Hawaii Superferry remains a subject of vigorous debate.

But a draft environmental impact statement released last week —while failing to satisfy some environmental groups —offers a reasonable guide to the risks and benefits of operating large-capacity ferries between the Hawaiian Islands.

The report points to the ferry as a practical alternative to moving people, vehicles and cargo, including local agricultural products, between the islands; the ferry also provides valuable transportation assistance when disaster strikes.

But the draft EIS also documents serious risks, particularly to humpback whales and the potential spread of invasive species. Indeed, both the state and Superferry have already begun work to mitigate those risks. That work and collaboration must continue, even in these difficult times.

The Superferry represents only a small fraction of inter-island transportation. But the EIS points out that its cargo — people with their cars and agricultural products — offers "a novel pathway for interisland dispersal of invasive species" among the islands.

That includes various types of grasses that can crowd out native and endangered flora, as well as destructive pests like fire ants and varroa mites.

That's important for the state Department of Agriculture to consider as it weighs its priorities under the pressure of budget cuts. The department, which trains and monitors Superferry inspectors, must ensure some level of oversight.

The Superferry, too, must maintain rigorous inspections of vehicles and cargo.

The EIS also recommended the Superferry seriously consider adopting an alternate route south of the Penguin Bank during the whale season. That's a reasonable proposal.

The draft EIS evaluated other potential negative impacts on traffic, cultural and recreational activities. But it suggested that with proper safeguards, a large-capacity ferry can have a future in Hawai'i. Proper inspections and sensible policies will help ensure that this is indeed the case.